Brake booster systems are generally known to assist a vehicle operator in applying force to a brake pedal by establishing a pressure differential across a diaphragm of a brake boosting device that is coupled to the brake pedal. During braking, chambers on each side of the diaphragm are separated such that a working chamber closest to the driver is at atmospheric pressure while the other side of the diaphragm is coupled to an engine air intake manifold and therefore may be at a lower pressure. Other configurations may further use an electrically-powered vacuum pump (EVP) to supply at least some brake booster vacuum. In still another approach described in US 2012/0096849 A1, boosted air from the air compressor of an engine turbocharger may be applied to the brake booster working chamber.
The inventor herein has recognized a disadvantage of these approaches in that a desired pressure differential across the diaphragm may not be maintained at all engine operating conditions or at all altitudes. For example, under certain engine operating conditions pressurized air from the turbocharger may not be available for the working chamber and ambient air pressure may vary with altitude. The inventor herein has addressed this issue by applying an exhaust pressure from a vacuum pump to the working chamber, and applying a vacuum pressure from the vacuum pump to vacuum chamber.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the Detailed Description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.